This invention relates to electret tapes and more particularly to improved apparatus for and a method of making such tapes.
U.S. Pat. No. 4,344,810 describes electret tape making apparatus in which Teflon covered layers on opposite sides of an electrically conductive strip are moved under and are electrostatically charged by a fluid saturated sponge-like electrode connected to a charging voltage. While the technique may be satisfactory at relatively low tape velocities of less than 1 centimeter per second, at higher velocities the dielectric liquid separates from the wet electrode and droplets form. As these droplets subsequently evaporate away from the electric field, electrostatic charges on the dielectric layer recombine under the droplets and form dead spots or voids, resulting in a defective electret tape.
This invention is directed to a solution of this problem.